Linear actuators in which a screw thread is used to convert a rotary motion into a linear motion are well-known. In U.S. Pat. No. 4,060,314 assigned to the same assignee as the present invention, there is described a high precision low friction linear actuator used in positioning and adjusting the reflecting surface of a laser mirror. The linear actuator shown in the patent utilized a screw thread and nut arrangement in which tiny ball bearings circulated in the threads between the screw and the nut to provide rolling friction between the threads of the screw and the nut. This actuator device derived its resolution and stability from the fact that the load was evenly distributed over a large number of ball-race contacts, and a high initial deflection of the ball-race contacts was provided by preloading of the actuator. Linear actuators of the type described in the above-identified patent, while extremely effective in operation, have several drawbacks in their design. First, because of the recirculating ball arrangement, it is difficult to reduce the size of the actuator, thus limiting the number of actuators that can be positioned in a given space. Manufacturing limitations on nut-race contours, ball recirculating mechanisms and other critical dimensions restrict practical screw diameters to a half-inch or larger for actuators of high precision. Secondly, the screw and nut arrangement has a load vector which is at an angle to the axis of rotation of the screw. Thus the load produces both a linear component of thrust and a radial component. For a given level of thrust produced by the linear actuator, a greater load is therefore imposed on the balls and ball-races than would be required if the full load were transferred in a direction parallel to the direction of the thrust.